Multiphoton single and double ionization of neon in the EUV

Abstract New information demonstrating the importance of both sequential and simultaneous (or direct) multiphoton ionization of inner shell electrons from neon is discussed in this paper. Ne was irradiated with intense 93 eV free electron laser (FEL) pulses at FLASH and studied with the aid of photoelectron spectrometry. This resulted in two and three photon, single and double ionization of neon, removing electrons from 2s and 2p subshells of the neutral Ne atom in multiple different pathways. The spectral features of the photoelectrons were identified through comparison with the NIST database and field averaged time-dependent density matrix theory. The calculations show the direct multiphoton ionization processes to be extremely sensitive to the focused FEL intensity.